A 1-day-old male neonate, born at term by vaginal delivery at 40+0 weeks of gestation, presented since birth with a left preauricular lesion that had not been detected during obstetric follow-up examinations.

A 3.5-cm erythematous-violaceous nodular lesion was observed, with firm consistency, smooth surface, and abundant fine vessels (Fig. 1).

Fig. 1

Ultrasound examination revealed a well-defined homogeneous hypoechoic solid lesion extending from the dermis to the muscular plane, with scarce Doppler flow (Fig. 1B). Whole-body magnetic resonance imaging (MRI) confirmed the solid nature of the lesion, which was intimately related to the parotid gland and the masseter muscle (Fig. 1C), and excluded the presence of additional lesions.

The tumor was excised en bloc at 11 days of life, achieving an excellent functional and cosmetic result. Histology demonstrated a multinodular biphasic proliferation composed of an outer layer of spindle cells immunohistochemically (IHC) positive for muscle actin (Fig. 2C), alternating with areas of more polygonal blast-like cells positive for CD34 (Fig. 2D) and vimentin, surrounding numerous staghorn vessels (Fig. 2B, arrows). Testing for PDGFRB mutation and t(12;15) translocation (ETV6 gene) was negative in the specimen.

Fig. 2

What is your diagnosis?

Solitary facial myofibroma.

The patient remained clinically stable, with no signs of local recurrence 1 year after excision.

Myofibroma is the most common fibrous tumor in infants, with an incidence rate of 1 in 150,000 live newborns.1 Up to 60% of these lesions are congenital.1 It usually presents as a solitary firm nodule (75%) involving the skin/subcutaneous tissue of the cephalic pole.1 However, it may occasionally appear as a clinically nonspecific lesion with abundant superficial vascularization, which may lead to an erroneous clinical diagnosis of congenital fibrosarcoma (up to 90% of which are associated with the ETV6-NTRK3 fusion gene) or congenital hemangiomas, among others.2–4 On the other hand, there is a multicentric form (myofibromatosis) with highly variable numbers of lesions and prognosis, since up to one-third of cases present visceral involvement. Therefore, systematic evaluation for organ involvement is always recommended, even in solitary myofibromas, preferably using whole-body MRI every 3–6 months within the first few years of life.5

Although generally sporadic, hereditary cases of myofibroma have been described, usually related to autosomal dominant germline mutations in the platelet-derived growth factor receptor beta (PDGFRB) gene, which also increase the risk of developing cerebral aneurysms.2,3 Therefore, some authors additionally recommend screening for such involvement during adolescence by means of brain MRI in mutation carriers.4 Furthermore, in a recent multicenter cohort of 69 patients, somatic mutations in the same gene were identified in sporadic cases of myofibroma.6 These somatic mutations, more frequent in multicentric myofibromas and apparently exclusive to the infantile form of the disease, have been associated with a greater response to tyrosine kinase inhibitors.2,3

Diagnosis of myofibroma requires histological confirmation, which typically demonstrates nodular infiltrates composed of an outer layer of myofibroblastic cells and an inner portion of polygonal/round cells with a hemangiopericytoma-like vascular pattern.4 Histology should be complemented with IHC techniques (generally positive for actin, vimentin, and occasionally CD34) and ideally PDGFRB sequencing.4 In contrast, germline mutation studies should be reserved for cases of multicentric myofibromas or those with significant familial aggregation.2,3

Since most congenital myofibromas undergo spontaneous involution within months, active treatment is generally unnecessary.4 Thus, surgery is reserved for complicated cases or those associated with aesthetic compromise, whereas chemotherapy (mainly vincristine/dactinomycin or vinblastine/methotrexate), either as monotherapy or as neoadjuvant/adjuvant therapy to surgery, is indicated in initially inoperable cases. In addition, as previously mentioned, good results have been reported with sunitinib and imatinib in some cases harboring PDGFRB mutations.2,3

The authors report no conflicts of interest.